06-08-2013, 04:28 PM
Surface Treatments
[attachment=57034]
Major Surface Treatments
Finishing and Polishing – covered previously
Coatings
Conversion Coatings (oxidation, anodizing)
Thermal Coatings (carburizing – flame spraying)
Metal Coatings (electrochemical, electroless)
Deposition
Physical Vapor Deposition
Chemical Vapor Deposition
Organic
Conversion Coatings – Phosphate Coating
Immersion in a Zn-P bath with Phosphoric acid causes growth of a crystalline zinc phosphate layer
Iron, Zinc or Manganese Phosphate layer formed
Typically applied to C-steel, low alloy steel and cast irons
Sometimes applied to Zinc, Cadmium, Aluminum and Tin
Typically very thin ~ 2.5 m
Conversion Coatings – Chrome Coating
Food cans
Immersion in a chromic acid bath (pH ~ 1.8) with other chemicals to coat surface
Known carcinogen chemicals used, so alternatives are currently under research
Molybdate chemicals currently best subsititute for aluminum coatings
Very good to minimize atmospheric corrosion
Many household goods – screws, hinges (yellow brown appearance)
Typically very thin < 2.5 m
Thermal Treatments – Surface Heat Treatment
Basic concept is to heat the surface to austenitic range, then quench it to form surface martensite - workpiece is steel
Heating Methods
Flame Treatment
Induction Heating
Copper coil wraps around part to heat by induction
Electron Beam or Laser Beam Hardening
Typically heat small area and allow the bulk solid heat capacity to quench the small heated area
Physical Vapor Deposition – Thermal PVD
Thermal PVD – also called Vacuum Deposition
Coating material (typically metal) is evaporated by melting in a vacuum
Substrate is usually heated for better bonding
Deposition rate is increased though the use of a DC current (substrate is the anode so it attracts the coating material)
Thin ~0.5 m to as thick as 1 mm.
Chemical Vapor Deposition
Deposition of a compound (or element) produced by a vapor-phase reduction between a reactive element and gas
Produces by-products that must be removed from the process as well
Process typically done at elevated temps (~900ºC)
Coating will crack upon cooling if large difference in thermal coefficients of expansion
Plasma CVD done at 300-700ºC (reaction is activated by plasma)
Typical for tool coatings
Applications
Diamond Coating, Carburizing, Nitriding, Chromizing, Aluminizing and Siliconizing processes
Semiconductor manufacturing
[attachment=57034]
Major Surface Treatments
Finishing and Polishing – covered previously
Coatings
Conversion Coatings (oxidation, anodizing)
Thermal Coatings (carburizing – flame spraying)
Metal Coatings (electrochemical, electroless)
Deposition
Physical Vapor Deposition
Chemical Vapor Deposition
Organic
Conversion Coatings – Phosphate Coating
Immersion in a Zn-P bath with Phosphoric acid causes growth of a crystalline zinc phosphate layer
Iron, Zinc or Manganese Phosphate layer formed
Typically applied to C-steel, low alloy steel and cast irons
Sometimes applied to Zinc, Cadmium, Aluminum and Tin
Typically very thin ~ 2.5 m
Conversion Coatings – Chrome Coating
Food cans
Immersion in a chromic acid bath (pH ~ 1.8) with other chemicals to coat surface
Known carcinogen chemicals used, so alternatives are currently under research
Molybdate chemicals currently best subsititute for aluminum coatings
Very good to minimize atmospheric corrosion
Many household goods – screws, hinges (yellow brown appearance)
Typically very thin < 2.5 m
Thermal Treatments – Surface Heat Treatment
Basic concept is to heat the surface to austenitic range, then quench it to form surface martensite - workpiece is steel
Heating Methods
Flame Treatment
Induction Heating
Copper coil wraps around part to heat by induction
Electron Beam or Laser Beam Hardening
Typically heat small area and allow the bulk solid heat capacity to quench the small heated area
Physical Vapor Deposition – Thermal PVD
Thermal PVD – also called Vacuum Deposition
Coating material (typically metal) is evaporated by melting in a vacuum
Substrate is usually heated for better bonding
Deposition rate is increased though the use of a DC current (substrate is the anode so it attracts the coating material)
Thin ~0.5 m to as thick as 1 mm.
Chemical Vapor Deposition
Deposition of a compound (or element) produced by a vapor-phase reduction between a reactive element and gas
Produces by-products that must be removed from the process as well
Process typically done at elevated temps (~900ºC)
Coating will crack upon cooling if large difference in thermal coefficients of expansion
Plasma CVD done at 300-700ºC (reaction is activated by plasma)
Typical for tool coatings
Applications
Diamond Coating, Carburizing, Nitriding, Chromizing, Aluminizing and Siliconizing processes
Semiconductor manufacturing